Machine

L’invention de la formule d’après laquelle les Brames calculent les éclipses suppose autant de science que la construction de nos éphémérides, et cependant ces mêmes Brames n’ont pas la moindre idée de la composition de l’univers ; ils n’en ont que de fausses sur le mouvement, la grandeur et la position des planètes, ils calculent les éclipses sans en connaître la théorie, guidés comme des machines par une gamme fondée sur des formules savantes qu’ils ne comprennent pas, et que probablement leurs ancêtres n’ont point inventées, puisqu’ils n’ont rien perfectionné et qu’ils n’ont pas transmis le moindre rayon de la science à leurs descendants : ces formules ne sont entre leurs mains que des méthodes de pratique, mais elles supposent des connaissances profondes dont ils n’ont pas les éléments, dont ils n’ont pas même conservé les moindres vestiges, et qui par conséquent ne leur ont jamais appartenu. Ces méthodes ne peuvent donc venir que de cet ancien peuple savant qui avait réduit en formules les mouvements des astres, et qui par une longue suite d’observations était parvenu non seulement à la prédiction des éclipses, mais à la connaissance bien plus difficile de la période de six cents ans et de tous les faits astronomiques que cette connaissance exige et suppose nécessairement.

Les plus grands changemens qu'ont éprouvés les plantations de cannes à sucre et les ateliers des sucreries ont eu lieu depuis 1796 jusqu'en 1800. On commença d'abord à substituer des manèges à mulets {trapiches de m'ilas] aux manèges à bœufs [trapiches de bucyea); puis, dans les Guines, on introduisit les roues hydrau- liques (trapiches de agua) , dont les premiers conquistadores avoient déjà fa.'t usage à Saint-Domingue; enfin (à Ceibabo), on essaya, aux frais du comte de Jaruco y Mopox, l'action des pompes à feu [bombas de vapor). De ces dernières machines, il y en a aujourd'hui 25 dans les différentes sucreries de l'île de Cuba. La culture de la canne à sucre d'Otahiti devint en même temps plus commune. On introduisit les chaudières

102 SECTION XV. Analysis of the Atmosphere—Its pressure—Law of Decrease in Density—Law of Decrease in Temperature—Measurement of Heights by the Barometer—Extent of the Atmosphere—Barometrical Variations—Oscillations—Trade-Winds—Cloud-Ring—Monsoons—Rotation of Winds—Laws of Hurricanes 117 SECTION XVI. Sound—Propagation of Sound illustrated by a Field of Standing Corn—Nature of Waves—Propagation of Sound through the Atmosphere—Intensity—Noises—A Musical Sound—Quality—Pitch—Extent of Human Hearing—Velocity of Sound in Air, Water, and Solids—Causes of the Obstruction of Sound—Law of its Intensity—Reflection of Sound—Echoes—Thunder—Refraction of Sound—Interference of Sounds 129 SECTION XVII. Vibration of Musical Strings—Harmonic Sounds—Nodes—Vibration of Air in Wind-Instruments—Vibration of Solids—Vibrating Plates—Bells—Harmony—Sounding Boards—Forced Vibrations—Resonance—Speaking Machines 140 SECTION XVIII. Refraction—Astronomical Refraction and its Laws—Formation of Tables of Refraction—Terrestrial Refraction—Its Quantity—Instances of Extraordinary Refraction—Reflection—Instances of Extraordinary Reflection—Loss of Light by the Absorbing Power of the Atmosphere—Apparent Magnitude of Sun and Moon in the Horizon 153 SECTION XIX.

SECTION XVII. Vibration of Musical Strings—Harmonic Sounds—Nodes—Vibration of Air in Wind-Instruments—Vibration of Solids—Vibrating Plates—Bells—Harmony—Sounding Boards—Forced Vibrations—Resonance—Speaking Machines. WHEN the particles of elastic bodies are suddenly disturbed by an impulse, they return to their natural position by a series of isochronous vibrations, whose rapidity, force, and permanency depend upon the elasticity, the form, and the mode of aggregation which unites the particles of the body. These oscillations are communicated to the air, and on account of its elasticity they excite alternate condensations and dilatations in the strata of the fluid nearest to the vibrating body; from thence they are propagated to a distance. A string or wire stretched between two pins, when drawn aside and suddenly let go, will vibrate till its own rigidity and the resistance of the air reduce it to rest. These oscillations may be rotatory, in every plane, or confined to one plane according as the motion is communicated. In the piano-forte, where the strings are struck by a hammer at one extremity, the vibrations probably consist of a bulge running to and fro from end to end. Different modes of vibration may be obtained from the same sonorous body.

A magneto-electric machine has been recently constructed by Mr. Henley, of enormous power. It consists of two permanent magnets, from which the induction is obtained; each of these is formed of thirty horseshoe steel magnets, two feet and a half long, and from four to five inches broad, and each is surrounded by a coil of wire six miles long, coated with silk to insulate the coils. A shock from these wires would be instantaneous death. This apparatus will ultimately be employed to send a stream of electricity through long submarine and subterraneous wires; but a Volta-electric machine has hitherto been used, in which the electricity is generated by a galvanic battery instead of magnets. Induction, or the effect of the spiral wires in augmenting the power of Voltaic electricity, is admirably illustrated in the Atlantic telegraph.

Ruhmkorff’s electro-inductive apparatus has either been improved, or new machines constructed, by Messrs. Grove, Gassiot, and Joule, of intense energy. Indeed, so great is the energy of electro-induction, that hopes were entertained of its superseding steam as a motive power. For the current of electricity from an electro-magnet can be made to flow in opposite directions, so as to produce alternate attractions and repulsions, and consequently a continued motion, which might be applied as a motive force to machinery. However, Mr. Joule has proved that the power developed by one pound of coal in combustion is to that produced by one pound of zinc consumed in Mr. Grove’s powerful electro-magnetic apparatus as nine to one, so that, even if zinc were as cheap as coal, and a Voltaic battery as easily kept in order as an engine-furnace, electricity will not supersede steam as a motive power. A current of electricity traversing a conductor gives out a quantity of heat determined by fixed laws, the amount of which is invariable as long as the machine to which it is applied remains at rest; but the instant the machine is set in motion a reaction takes place in the intensity of the current, causing a diminution in the quantity of heat, because the heat that disappears is converted into the mechanical force exerted by the engine.

But as soon as the plate is inclined to that plane, electricity begins to be developed by its motion across the lines of magnetic force; it becomes more powerful as the inclination increases, and arrives at a maximum when the plate revolves at right angles to the line of dip. When the revolution is in the same direction with that of the hands of a watch, the current of electricity flows from its centre to the circumference; and when the rotation is in a contrary direction, the current sets the opposite way. Thus a copper plate, revolving at right angles to the line of the dip, becomes a new electrical machine, differing from the common plate-glass machine by the copper being the most perfect conductor, whereas glass is the most perfect non-conductor; besides insulation, which is essential to the glass machine, is fatal to the copper one. The quantity of electricity evolved by the metal does not appear to be inferior to that devolved by the glass, though very different in intensity. Even a ship crossing the lines of force must have electric currents running through her. Dr. Faraday observes that such is the facility with which electricity is generated by the magnetic lines of force, that scarcely any piece of metal can be moved without a development of it; consequently, among the arrangements of steam-engines and metallic machinery, curious electro-magnetic combinations probably exist which have never yet been noticed. Thus magnetic lines of force certainly issue from the surface of the globe.

James, Colonel, measurements of, in the General Survey of Great Britain, 47; density of the earth determined by, 58. Jamin, M., remarks of, on substances producing elliptical polarization, 193. January, epoch of its beginning the year, 85. Jews, denominations of time in their calendars, 85. Josephstadt, discovery of a comet from, 367. Joule, Mr., heat considered a mechanical force by, 275; his view of elastic force, 276; amount of latent force in a pound of coal, computed by, 278; furnishing data to Professor Thomson, 279; quantity of heat generated in a unit of time by electricity computed by, 302; powerful magnet obtained by electricity, 315; electric machines constructed by, 328; experiments proving heat and mechanical power convertible, 329. Jovial system, mass of the whole, 55. Julian Calendar, year of, the first of our era, 86. June, 1833, reappearance of Saturn’s rings, 67; coincidence of times in, 84. Juno, the diameter of, 56; astronomical tables of, 63.

Magneto-electricity, principle suggesting, 322; machine constructed on the principle of, 325; relation of heat to, 329. Magnets, influence of, on electric light, 307; fish possessing the power of making, 311; effect of an electric stream on, 312-314; obtained by electricity, 315; power of electro, measured, 315; cylinders acting as, 316, 317; producing electrical effects, 322, 323; evolving electricity by rotation, 330; classification of substances in relation to, 332; polarity a property of, 336; effect on themselves of imparting paramagnetism, 337; experiment showing the lines of force of, 338; properties of, indestructible by subdivision, 338, 339; the earth reckoned among, 342; planets reckoned among, 346; action of an electro, on copper, 351. Maguire, Captain, his observations on magnetic storms, 345, 346. Malo, St., rising of the tide at, 98. Malus, M., discovery of polarization of light by, 195; attempts of, to polarize heat, 264. Malta, observations on Saturn’s rings made at, 66. Manchester, thunderstorm near, in 1835, 292. Mankind, distinct tribes of, 255; limited perceptions of, 267. Marcet, M., rate of increase in temperature below the earth’s surface calculated by, 230. Marco Polo, atmospheric effects observed by, in ascending mountains, 118.

Waterspouts, origin and cause of, 128. Waterstone, Mr., magnetic property of the ethereal medium maintained by, 357. Waves neutralized by interference, 99. ——, atmospheric, over local districts, periods, dimensions of, 121, 122. —— of sound, 131; furnishing an illustration of reflections of sound and light, 137; interference of, producing calm, 139. Wedgwood, Dr., attempts of, to trace objects by means of light, 203, 204. Week, the, of seven days, the most ancient and universal division of time, 85. Wells, increase of temperature in, 230, 231. Welsh, Mr., observations made by, in a balloon ascent, 119. West Indies, the, cause of hurricanes in, 126. Wheels invented to test intensity of sound, 132, 133. Wheat, range of its cultivation, 250. Wheatstone, Professor, experiments in acoustics of, 132; musical instruments invented by, 143; paper on musical vibrations read by, 145; experiments on sounding boards of, 150; experiments on sound reinforced by resonance, 151; instrument measuring velocities of electricity and light invented by, 202; spectrum of an electric spark observed, 289; speed of electricity measured, 289, 290; experiments on the spectrum of Voltaic flame, 303. Willis, Mr., articulating machine invented by, 151; investigations of, into the mechanism of the larynx, 152.